Military deceptionis defined as those actions executed to deliberately mislead adversary decision makers as to friendly military capabilities, intentions, and operations, thereby causing the adversary to take specific actions (or inactions) that will contribute to the accomplishment of the friendly mission. It is an attempt to amplify, or create an artificial fog of war or to mislead the enemy using psychological operations, information warfare and other methods. It overlaps with psychological warfare to the degree that any enemy that falls for the deception will lose confidence when it is revealed, and may hesitate when confronted with the truth.

Before D-Day, Operation Quicksilver portrayed "First United States Army Group" (FUSAG), which was merely a skeleton headquarters commanded by General Omar Bradley, as a genuine large army group commanded by General George Patton. In Operation Fortitude South, the Germans were then persuaded that FUSAG would invade France at the Pas-de-Calais. British and American troops used false signals and the messages of double agents to deceive German intelligence organizations and radio intercept operators. Contrary to popular myth, dummy equipment played a negligible role in the operation, for the Germans were unable to mount reconnaissance over English territory in the face of total Allied control of the air. This had the desired effect of misleading the German High Command as to the location of the primary invasion, thus inducing them to keep reserves away from the actual landings. Erwin Rommel and Hitler himself were the primary targets of this operation: convinced that Patton would lead the invasion, Rommel was caught off guard and unwilling to react strongly, as Patton's illusionary FUSAG had not yet landed. The Germans awaited this landing for many crucial weeks, finally concluding that it would not take place because of Allied success in breaking out from the Normandy bridgehead. Confidence and speed was reduced enough that the German response to the beachhead was weaker than it would otherwise have been.

These two cases alone demonstrate the extreme importance of military deception in outcomes of major historical battles.

During World War II, The London Controlling Section, a British organization, and the Joint Planning Staff, the US counterpart, were responsible for devising and coordinating cover and deception plans.

An example of huge-scale maskirovka in the Soviet Union was false maps, with distorted locations of settlements, road forks, river shapes, etc. Public transportation maps of cities, while showing correct interaction of traffic routes, were distorted in general appearance.[2] What is more striking is that distance indicators on highway road signs gave false numbers. All this was supposed to confuse a potential invader.

The value of military deception is subject to a difference of opinions among military pundits. For example, the two books that are usually considered the most famous classics on warfare Sun Tzu's The Art of War and Clausewitz' On War seem to have diametrically opposed views on the matter. Sun Tzu greatly emphasizes military deception and considers them the key to victory.[3] Clausewitz on the other hand argues that a commander has a foggy idea of what is going on anyway[4] and that creating some sort of false appearance, particularly on a large scale, is costly and can only be acceptable from a cost-benefit-analysis point of view under special circumstances.[5]

As a more modern example, the British military writer John Keegan seems to come close to Clausewitz' opinion in this particular matter, despite normally being highly critical of Clausewitz. In his book Intelligence in War: Knowledge of the Enemy from Napoleon to Al-Qaeda he gives several historical examples of situations where one side held a great information advantage over his opponent and argues that in none of these cases were this decisive in and of itself for the outcome.

Thaddeus Holt, "The Deceivers: Allied Military Deception in the Second World War" (A Lisa Drew Book/Scribner, 2004) ISBN 0-7432-5042-7

Michael Howard, "Strategic Deception in the Second World War: Brithish Intelligence Operations Against the German High Command" (W. W. Norton & Co., First published as a Norton paperback by arrangement with HMSO, 1995) ISBN 0-393-31293-3